Catalyst regeneration apparatus

ABSTRACT

Regeneration of spent catalyst contaminated by a carbonaceous deposit is conducted by contacting the spent catalyst with a hot flue gas emanating from a first dense phase regeneration zone. The heated spent catalyst is then contacted countercurrently with an oxygen-containing gas in the first dense phase regeneration zone to produce partially regenerated catalyst which is subsequently contacted concurrently with an oxygen-containing gas in a second dense phase regeneration zone. The regenerator includes a standpipe section disposed within the regeneration vessel in concentric relation to the vertical axis thereof with a cylindrical baffle disposed around an upper portion of the standpipe section. The baffle has at least one orifice at its lower portion for direct passage of catalyst from the fluidized bed into the annular zone between the baffle and the standpipe. The catalyst inlet means to the regenerator is positioned at a spaced distance above the standpipe, whereby ctalyst is introduced above the fluidized bed.

This is a division of application Ser. No. 451,805, filed Mar. 18, 1974now U.S. Pat. No. 3,902,990.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process and apparatus for regenerating spentcatalyst utilized in hydrocarbon conversion processes. The invention isapplicable to fluidized systems wherein finely divided catalyst iscontinuously recycled between a reaction zone and a separateregeneration or reactivation zone. It is particularly applicable to theregeneration of spent fluid catalytic cracking catalyst.

2. Description of the Prior Art

Catalytic hydrocarbon conversion processes wherein a catalyst that hasbecome partially inactivated due to carbonaceous deposits is regeneratedby combustion with an oxidizing gas and in which the regenerationcatalyst is recycled to the reaction zone are well known to thoseskilled in the art.

It is also known that spent catalyst can be regenerated in more than onestage of regeneration (see, for example, U.S. Pat. No. 3,767,566 andHydrocarbon Processing, September 1972, page 136).

In such prior art processes, the sensible heat of the flue gas producedby the combustion of the carbonaceous deposit of the catalyst is lost tothe process. Furthermore, currently, a large degree of afterburn ispracticed in some units to keep the carbon monoxide effluent from theregenerator at an absolute minimum. This afterburn is produced since theunit has a large amount of oxygen leaving the top of the bed and theresidual carbon monoxide leaving the bed is burned in the dilute phasezone above the bed where little catalyst is present. Since there is nocatalyst heat sump, the temperature rises as much as 140° to the 1400°F.± level. Since it is desirable to minimize temperature from thestandpoint of minimizing thermal deactivation of the catalyst, any meansto reduce this temperature will result in more active catalyst andimproved yields of gasoline or improved conversion. The presentinvention will lower the temperature in the upper part of theregenerator and thereby reduce the degree of afterburn.

Additionally, it is now necessary to quench the regenerator off-gases toabout 1200°F. due to temperature limitations on the blading of flue gasexpanders or to prevent using very costly alloy materials in the fluegas circuit. The quench is usually a water spray. This spray results ina direct loss of energy from the process due to the unrecoverable heatof vaporization. The present invention will eliminate the need for thisspray.

It has now been found that improved results can be obtained in acatalyst regeneration process carried out in a specified manner.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided, in a process forthe catalytic conversion of hydrocarbons in a fluidized reaction zonewherein the spent conversion catalyst is separated from the reactionzone effluent, stripped of volatile hydrocarbons, regenerated bycombustion of carbonaceous deposits and recycled to the reaction zone,the improvement which comprises: contacting the stripped spent catalystin a dilute phase zone with a hot flue gas emanating from a first densephase regeneration zone to heat said stripped spent catalyst and coolsaid hot fluid gas; contacting the heated stripped catalyst with anoxygen-containing gas in said first dense phase regeneration zone toeffect partial regeneration of said catalyst, and contacting thepartially regenerated catalyst concurrently with an oxygen-containinggas in a second dense phase regeneration zone.

Furthermore, in accordance with the invention, there is provided, in aregenerator vessel adapted to contain a bed fluidized catalyst, whichcomprises: a section of a standpipe having an enlarged diameter open andforming an overflow well for withdrawing regenerated catalyst from saidregenerator vessel, said standpipe section being disposed in concentricrelation to the vertical axis of said regenerator vessel; catalyst inletmeans; gas outlet means, and gas inlet means, the improvement whichcomprises; a cylindrical baffle disposed around an upper portion of saidstandpipe section, said baffle comprising at least one orifice at itslower portion for direct passage of catalyst from said dense bed into anannular zone formed by said cylindrical baffle and said section ofstandpipe, and means for introducing a gas into said annular zone.

The baffling of the present invention promotes general countercurrencyof catalyst flow with regenerator gas flow in the major portion of theregenerator bed. It permits quenching of the gases leaving the bed at1200° to 1400°F. with the relatively cooler spent catalyst of 900° to1100°F. It also prevents the direct short circuiting of the spentcatalyst across the top of the bed to the top of the overflow well andout of regenerator. The baffle may have a conical top to keep thecatalyst which is raining down out of the dilute phase zone(deentrainment) from falling into the top of the well and thus shortcircuiting the bed.

Other methods are available for accomplishing staging, such as, separatevessels, or totally baffled vessels or partially baffled vessels.

These known methods have many disadvantages. For a separate vesselstaging method, there is the need for a separate additional catalysttransport conduit and large investment in an extra vessel and catalystrecovery equipment. For a fully baffled vessel, there is the problemthat there may be an unbalance of gas flow on either side of the bafflethus overloading the catalyst recovery equipment on one side andunderloading on the other. Some regenerators have been shown to havebaffles extending up the vessel to slightly above the bed level. Thereis much catalyst carried up into the dilute phase above the bed whichfalls back to the bed. Such a baffle does not prevent crossover of thedeentrained material which can reduce the effectiveness of the staging.In none of these partially shrouded vessels is the spent catalystintroduced to the dilute phase above the primary regeneration bed.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates, in schematic form, a suitable apparatus for carryingout a preferred embodiment of the invention.

FIG. 2 is an enlarged view of the regenerator vessel of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment will be described with reference to theaccompanying drawing and as applied to catalytic cracking ofhydrocarbons, for simplicity, but it should be understood that theinvention is equally applicable to other hydrocarbon conversionprocesses such as naphtha reforming, hydrogeneration, dehydrogenation,isomerization, etc., provided that appropriate catalyst and operatingconditions be employed as required for the particular conversionprocess.

Referring to FIG. 1, a suitable hydrocarbon feed is injected via line 10into transferline riser 12 which contains hot regenerated catalyst. Uponinjection, the hydrocarbon feed is vaporized by contact with the hotcatalyst. The resulting suspension of vaporized hydrocarbon and catalystflows upwardly through the straight vertically disposed transferlineriser where at least a portion of the hydrocarbon feed is cracked tolower boiling products. The density of the catalyst in the suspensionmay range generally from about 0.5 to about 10 pounds per cubic foot,preferably, from about 1 to 4 pounds per cubic foot. The suspensionpasses through the transferline riser (reactor) at a velocity betweenabout 8 and 60 feet per second. The catalyst hold-up in the transferlineriser, using conventional silica-alumina cracking catalyst of the sizebetween 10 and 300 microns with an average particle diameter of about 60microns, may be between 1 and 12 tons for a 50,000 barrels per day unit.The pressure in the transferline riser may be between 9 and 40 poundsper square inch gauge (psig), for example, about 35 psig. The crackingtemperature in the transferline riser may be between 825° and 1150°F.,with the temperature at the inlet being higher than at the outlet of thetransferline riser. Suitable space velocity in the transferline risermay range from about 25 to about 150 weight parts of hydrocarbon feedper hour per weight part of catalyst, and the catalyst to oil weightratio may be between 2 and 12. The length to diameter (L/D) of thetransferline riser may be between 6 to 30. Desirably, the length todiameter ratio of the transferline riser is such as to provide 3 secondsof gas resistance when the gasiform suspension of catalyst flows throughthe transferline at an average velocity of about 30 feet per second. Thetransferline riser projects upwardly into the lower portion of agas-solids disengaging vessel 14 and terminates beneath distributinggrid 16. Vessel 14 is positioned at a spaced distance and adjacent toregenerator vessel 30. Desirably, at least a portion of it is alsopositioned at a higher level than the top of vessel 30. The riser entersinto the bottom cone of vessel 14 directly under grid 16 which is weldeddirectly to the vessel shell. The suspension passes into a dense bed offluidized catalyst having a level indicated at 18 where furtherhydrocarbon conversion occurs. The cracked hydrocarbon vapors passthrough the upper level of the dense fluidized bed into a superimposeddilute phase and cyclone separator (not shown) disposed in the upperportion of vessel 14, to separate product vapors from entrained catalystparticles. The catalyst particles are returned to the dense bed viacyclone diplegs and the product vapors are removed via product outletline 20. Desirably, the cyclone separator may be a two-stage cyclonesystem. Alternatively, when increased gasoline boiling range product isdesired, the dense fluidized bed may be omitted in vessel 14 and thetransferline may be extended into the vessel such that the mainconversion of hydrocarbons may occur in the transferline. In thisalternative embodiment, the transferline may also terminate directly ina cyclone separator. The lower portion of vessel 14 comprises astripping zone 22 in which hydrocarbons which adhere to spent catalystare removed by stripping with a stripping gas, such as, steam introducedvia line 24. Desirably, grid 16 is sloped to facilitate the flow ofspent catalyst into stripping zone 22. The stripping zone is offset 180°from the transferline entrance into vessel 14. The pressure balance ofthe unit will allow the catalyst level in the stripping zone to be heldeither somewhat above grid 16 to provide a higher hold-up operation orit can be held very low in the stripping zone so as to provide dilutephase stripping. Spent stripped catalyst flows from tjhe stripper viacontrol valve 26 into conduit 28 which terminates in regenerator vessel30 in a dilute phase zone above upper level 32 of a dense fluidized bedof catalyst undergoing regeneration in the lower portion of theregenerator vessel. As the stripped spent catalyst is discharged fromconduit 28, it flows in a downward direction and is contacted by a hotupflowing flue gas which emanates from the dense fluidized regenerationbed. The catalyst is heated and the flue gas correspondingly cooled bythis direct heat exchange. The heated catalyst continues to flow downinto the dense fluidized regeneration bed which is maintained at atemperature ranging from about 1100° to about 1400°F. and at a pressureranging from about 10 psig to about 50 psig. An oxygen-containing gas(air) is introduced via line 34 into an auxiliary burner 38 attached tothe bottom of the regenerator vessel for heating the unit on start-up ofthe process. The oxygen-containing gas flows from the auxiliary burnerinto the interior bottom portion of the regenerator and passes throughperforated grid 33 into the dense fluidized bed, at a superficial vaporvelocity sufficient to maintain the catalyst particles above grid 33 asa dense fluidized bed and to produce the desired level of regeneration.Suitable superficial vapor velocity includes a range of about 2 feet persecond to about 6 feet per second. By superficial vapor velocity isintended herein the linear velocity that the gas would have provided nosolids were present in a given zone. Flue gas formed by combustion ofthe carbonaceous deposit and entrained solids pass through a cycloneseparator system (not shown) disposed in the regenerator. Solids arereturned via cyclone dipleg to the fluidized bed while flue gases areremoved overhead via line 36. A cylindrical baffle 50 is positioned inthe dense fluidized regeneration bed in spaced concentric relation tothe wall of the regenerator shell. Cylindrical baffle 50 is providedwith a number of orifices 52 in its lower portion. The upper portion ofthe baffle terminates in a conical section 54 having a central hole 56.Cylindrical baffle 50 surrounds an overflow well 40 located on thecenterline of the regenerator vessel. The well serves to hold thecatalyst level constant in the regenerator. The well is the open upperend of a downflow withdrawal standpipe 42 which extends into theregenerator vessel. The partially regenerated catalyst flows from thedense regeneration bed through orifices 52 into an annular zone 58formed by cylindrical baffle 50 and the section of standpipe 42 whichextends through cylindrical baffle 50. A portion of theoxygen-containing gas which was introduced into the regenerator vesselflows through the perforated grid 33 into annular zone 58. The gascontacts the partially regenerated catalyst concurrently and completesthe desired degree of regeneration by combustion of an additional amountof carbonaceous deposit from the catalyst, as well as, moves thecatalyst particles upwardly.

A coil with holes 61 for distribution of an oxygen-containing gas can beprovided in the bottom of the annular zone so as to permit control ofthe degree of regeneration occurring in the annular zone. Theoxygen-containing gas may be introduced via holes 61 into the annularzone, for example, at a superficial velocity ranging from about 2.5 feetper second to about 4.5 feet per second.

The temperatures in the annular zone 58 (which functions as a seconddense phase regeneration zone) is maintained at a temperature of about1120° to about 1410°F. The temperature rise is dependent upon the amountof additional regeneration accomplished. Flue gas exits through orifice56 of the conical top of cylindrical bafffle 50 and regenerated catalystflows into overfow well 40. The conical top of the cylindrical baffleserves to prevent spent catalyst from falling into the interior ofcylindrical baffle 50. A deflector 60 is provided at a spaced distanceabove orifice 56 to assist in keeping spent catalyst from falling intocylindrical baffle 50.

The regenerated catalyst which has been moved upwardly in annular zone58 to the top of overflow well 40, flows into the well and moves downthrough standpipe 42 which is connected at its lower end by means ofangle bend 43 with a vertically inclined conduit 44 which in turnconnects with vertical transferline riser 12 which has a sectionprojecting upwardly into vessel 14 as previously described. Aerationtaps 46 in which a fluidizing gas, such as, steam may be injected, areprovided along vertically inclinded conduit 44. Desirably, thevertically inclined conduit is sloped at an angle of about 45°. Ifdesired, a shut-off valve 48 may be provided at the entrance of thevertically inclined conduit into riser 12 or alternatively, it may beinstalled at the bottom of standpipe 42 for use in start-up of the unitor in an emergency. This shut-off valve will always be either wide openor closed tight since it is not required for actual regulation ofcatalyst circulation when the unit is in operation. This valve may belocated essentially anywhere along the length of riser 12 or anywherealong the length of standpipe 42. Instead of a shut-off valve, a ceramiclined restriction orifice may be used.

A specific example of the heat balance of the regeneration process ofthe invention is as follows:

If the catalyst circulation is 21.6 tons per minute and the reactionzone temperature is 900°F., a 1400°F. flue gas emanating from theregeneration dense bed would heat the spent 900°F. catalyst particlesintroduced from the reactor into the regenerator to about 966°F., whilecooling the flue gas to 966°F. The calculated heat recovered in theregenerator under the conditions given in this example is 42 M BTU/hr.This heat would normally be carried out with the flue gas.

What is claimed is:
 1. In a regenerator vessel adapted to contain a bedof fluidized catalyst, which comprises: a section of a standpipe havinga enlarged diameter open end forming an overflow well for withdrawingregenerated catalyst from said regenerator vessel, said standpipesection being disposed in concentric relation to the vertical axis ofsaid regenerator vessel; catalyst inlet means; catalyst outlet means;gas outlet means, and gas inlet means, the improvement which comprises:a cylindrical baffle disposed around an upper portion of said standpipesection, said baffle comprising at least one orifice at its lowerportion for direct passage of catalyst from said fluidized bed into anannular zone formed by said cylindrical baffle and said section ofstandpipe, and means for introducing a gas into said annular zone, saidcatalyst inlet means being positioned at a spaced distance above saidstandpipe, whereby said catalyst is introduced above said bed offluidized catalyst.
 2. The regenerator of claim 1 wherein saidcylindrical baffle comprises a conical top section having a gas outletorifice at its upper end.
 3. In the regenerator of claim 1, the furtherimprovement comprising a deflector positioned in spaced relation abovesaid cylindrical baffle.
 4. The regenerator of claim 1, wherein saidmeans for introducing a gas into said annular zone comprises a pipepositioned in the bottom of said annular zone.